The invention relates generally to switches for interrupting the flow of electrical current and, particularly, to a vacuum switch for high-voltage circuits, and, still more particularly, to a new and improved current interchange for providing a current path to the movable contact of a vacuum switch.
Vacuum switches are used in a variety of applications. A vacuum switch may be used for capacitor switching or for sectionalizing a line or system of switches. A vacuum switch may also be molded into a "loadbreak" elbow connector to interrupt currents of medium voltage distribution systems. A vacuum switch may also be molded into a solid insulator or be used in a switch enclosure under oil. Typically, vacuum switches are employed as a high-voltage vacuum circuit interrupter.
Loadbreak switches used in voltage power distribution range circuits are of four general types, namely air brake switches, oil insulated switches, gas insulated switches, and vacuum interrupters. The present invention is particularly applicable to high-voltage vacuum-type circuit interrupters which are well known in the art. As used herein, the term "high-voltage" means a voltage greater than 1,000 volts. In such switches, the contacts are enclosed in an evacuated chamber. The vacuum environment rapidly dissipates the gaseous products of the arc drawn between the contacts of the switch to effect interruption of the current when the switch is open.
Typically, a vacuum circuit interrupter includes a pair of electrodes, one being stationary and the other movable between an open and closed position to open and close the circuit. Although vacuum circuit interrupters may be used in either a single-phase or three-phase system, they are commonly used in a three-phase system with multiples of three switches mounted in a common grounded metal enclosure. U.S. Pat. Nos. 3,048,681; 3,048,682; 3,586,801; 3,777,089; and 4,158,911 illustrate vacuum circuit interrupters having opposed electrodes, one being stationary and the other being movable. Such patents also disclose metallic shields to shield portions of the interior of the housing of the interrupter from the metal on the electrodes which is vaporized upon the creation of the resulting arc upon opening a gap between the electrodes to open the interrupter.
U.S. Pat. No. 4,568,804 discloses a high-voltage vacuum type circuit interrupter. The interrupter includes a ceramic insulating housing mounted on a metallic base and a lower housing which includes an actuator. A vacuum module having a housing with an evacuated environment is disposed within the ceramic insulating housing and includes a pair of switch contacts. One switch contact is stationary and is electrically connected to a top or switch electrical terminal. The other contact is movable and is electrically connected to a line terminal and electrical ground. A dielectric operating rod is connected to the movable switch contact and to the actuator. The switch contacts are mounted within a metallic vapor shield. A metallic bellows is used to seal the lower movable contact.
Another form of a vacuum switch is shown in U.S. Pat. No. 2,981,813. Two opposed stationary contact rods extend into a hermetically sealed and vacuumized envelope with a gap between the terminal ends thereof. A contact means in the form of a copper disc is mounted on an actuator shaft. The actuator shaft includes a dielectric post having one end affixed to the contact means and the other end affixed to a metallic rod extending through an expansible metallic bellows and through an aperture in the envelope for connection to an operating means for actuating the contact means. The dielectric post electrically insulates the contact means from the rod and bellows. One end of the bellows is hermetically sealed with the envelope and the other end is connected to the inner end portion of the rod.
As shown in U.S. Pat. No. 4,568,804, the interrupter includes an elongated, dielectric operating rod having a movable switch contact disclosed at its uppermost longitudinal end. The movable switch contact is movable relative to a stationary or fixed switch contact so as to open or close the electrical circuit path between two terminals. The operating rod is actuated by an actuator member such as the solenoid operated toggle mechanism shown in the '804 patent. The '804 patent teaches a conductive contact stem mounted on the end of the operating rod. A direct electrical connection is maintained between the contact stem of the movable switch contact and one of the side terminals. The '804 patent teaches a contact block which maintains electrical engagement with the movable contact stem and the side terminal. A metallic bellows has one movable end fixed to the contact stem and another stationary end fixed to the housing to preserve the vacuum during the movement of the movable switch contact.
U.S. Pat. No. 4,124,790 teaches a current transfer assembly for the movable contact. Other patents, such as U.S. Pat. Nos. 3,025,375 and 3,471,669, teach shunts or connecting leads extending between the movable contact and terminal.
Various other methods of forming the electrical current path between the moving rod and terminal include straight wire cords, interleaved copper foil, garter spring sliding contacts, a mercury well, and a moving link. However, such prior art devices have not been compact and require substantial inertia and force to reciprocate the moving rod between the open and closed positions. Because of the length requirements of the vacuum switch, the straight wire cords tend to apply a resistive force to the contact stem at either end of the stroke. The interleaved copper foil includes approximately 100 layers of one-thousandths inch thick copper foil approximately an inch wide. This copper foil has the same deficiency as that of the straight wire cords.
The present invention is compact both in the axial and radial directions and is shorter both in length and radial dimension as compared to the prior art. The present invention includes a low inertia and low force interrupter that provides an electrical current path between the moving contact stem and a terminal of the vacuum switch. Further, the present invention provides a means of sealing the encapsulation die during production. The present invention overcomes the deficiencies of the prior art.